Aircraft deicing systems are well-known and widely used safety devices for the removal of ice accumulated on aerodynamically significant aircraft surfaces, such as propeller and helicopter rotor blade airfoils. It has been found that cycling the application of heat to the leading edge of the airfoil in cordwise or spanwise segments results in substantially improved ice shedding characteristics with significantly reduced energy requirements. Accordingly, most present-day aircraft deicing systems incorporate a plurality of electrical resistance-type heating elements, known as deicing segments, which are sequentially and cyclically energized in symmetrical sets on opposing blades.
In order to selectively energize each deicing segment, a separate electrical connection was necessary for each opposing pair of deicing segments and a single additional electrical connection, common to all deicing segments, was required to complete each two-wire deicing segment circuit. Unfortunately, the energy requirements of these deicing segments are such that power must be obtained from one of the electrical power generators located elsewhere on the aircraft. Thus, some mechanism is required for coupling the power from the aircraft's fixed generating system to the rapidly rotating propeller or rotor blades. Historically, a suitable plurality of brush block assemblies were rigidly mounted to the aircraft, and slip-ring assemblies positioned on the rotating propeller or rotor drive shaft to effectuate this coupling. More recently systems have been developed which permit the sequential distribution of electrical power to any number of deicing segments with only two separate slip-ring assemblies, as evidenced by U.S. patent application Ser. No. 009,636 filed Feb. 5, 1979, now U.S. Pat. No. 4,292,502, and owned by the assignee of the present invention. However, irrespective of their number, such assemblies are subject to substantial wear, require frequent maintenance and replacement and, in large part due to vibrational and impulse loads placed thereon, present a constant threat of in-flight deicing system failure.
In an effort to minimize the difficulties that arise in conducting an electrical signal between a fixed frame and a member rotating with respect thereto, a manufacturer doing business as Mercotac, Inc. of San Diego, Calif. has designed a four conductor sealed power transfer units having the model designation Mercotac 540 for transferring both signal and power level currents required by the helicopter deicing system elements. However, the Mercotac 540, even more so than conventional slip-ring assemblies, cannot withstand vibrational and impulse loads without significant degradation in performance, vastly accelerated breakdown rates and much shorter times to total failure. Accordingly, it is not believed that any successful attempt has previously been made to adopt power transfer units other than conventional slip-ring assemblies to the transfer of electrical power from a helicopter power system to helicopter deicing segments.